CATALYTIC OXIDATIONS: HETEROGENEOUS CATALYTIC OZONATION AND THE REACTION OF DIOXYGEN WITH OSMIUM-CARBOHYDRATE POLYMERS (CLOCK REACTION).

摘要

The study consists of two parts: The first is a short study on heterogeneous catalytic ozonation. In this study various species that may be involved in surface catalyzed ozonation are examined. It is suggested that a surface ozonide is formed in the heterogeneous process which decomposes into radical species and initiate a radical chain mechanism in the substrate oxidation.; In the second part, the general reactions between osmium-carbohydrate polymers, termed osmarins, with dioxygen is studied. Osmarins have been earlier proposed as potential antiarthritic drugs. Many of the antiarthritic agents are believed to catalytically remove reactive oxygen species in aerobic in vivo processes which has been held responsible for rheumatoid arthritis and similar biodegradations. Osmarins have also demonstrated a rich and varied oxygen chemistry.; Osmarins, which are intensely colored substances, lose color when reacted with dioxygen in aqueous solutions. In the present study reactions of osmarins with dioxygen in basic aqueous solutions were followed by monitoring the absorbance changes at 480 nm. After a small initial rise, the absorbance changes at 480nm. After a small initial rise, the absorbance went through an induction period during which the absorbance decreased very slowly to about 60% of its initial value. At the end of this period the absorbance fell off drastically.; The absorbance changing patterns for all osmarins preparations in general behaved as a clock reaction and was treated as such. The induction periods were taken as the clock times, t(,2). While the orders with respect to OH('-) and dioxygen pressure for various osmarin preparation were estimated as approximately 0.2 and 1, respectively, a two-term expression was proposed for t(,2) (= k(,1)C + k(,2)C('-1/3)). The first term expressed a zero order rate dependence on osmarin concentration while the second term involved the diffusion rate of dioxygen into the aqueous phase to encounter the osmarin molecules. The apparent activation energies were estimated as 10-15 Kcals/mole. A general expression was formulated based on a similar treatment to predict the mass specific clock times, defined as clock time per unit concentration. Possible mechanism involving an OsO(,4) catalyzed process was discussed.